Do the Atlantic Ocean and the Pacific Ocean Mix. Types of Agate With Photos Rubellite – Properties, Value, Occurrence and Uses New York Rockhounding – Places to Dig for Crystals in New York Types of Opal With Photos The Mystery of the Copper Scorpion.

Do the Atlantic Ocean and the Pacific Ocean Mix.

Do the Atlantic Ocean and the Pacific Ocean Mix.

Types of Agate With Photos.

Rubellite – Properties, Value, Occurrence and Uses.

New York Rockhounding – Places to Dig for Crystals in New York.

Types of Opal With Photos.

The Mystery of the Copper Scorpion.

The Mystery of the Copper Scorpion.

The Ring of Fire.

The Rarest Mineral on Earth.

Continental crust is the layer of igneous, metamorphic, and sedimentary rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its bulk composition is richer in aluminium silicates (Al-Si) and has a lower density compared to the oceanic crust, called sima which is richer in magnesium silicate (Mg-Si) minerals.

Most continental crust is dry land above sea level. However, 94% of the Zealandia continental crust region is submerged beneath the Pacific Ocean, with New Zealand constituting 93% of the above-water portion.

The continental crust consists of various layers, with a bulk composition that is intermediate (SiO2 wt% = 60.6). The average density of the continental crust is about, 2.83 g/cm3 (0.102 lb/cu in), less dense than the ultramafic material that makes up the mantle, which has a density of around 3.3 g/cm3 (0.12 lb/cu in).

At 25 to 70 km (16 to 43 mi) in thickness, continental crust is considerably thicker than oceanic crust, which has an average thickness of around 7 to 10 km (4.3 to 6.2 mi). Approximately 41% of Earth’s surface area and about 70% of the volume of Earth’s crust are continental crust.

Because the surface of continental crust mainly lies above sea level, its existence allowed land life to evolve from marine life. Its existence also provides broad expanses of shallow water known as epeiric seas and continental shelves where complex metazoan life could become established during early Paleozoic time, in what is now called the Cambrian explosion.

All continental crust is ultimately derived from mantle-derived melts (mainly basalt) through fractional differentiation of basaltic melt and the assimilation (remelting) of pre-existing continental crust. The relative contributions of these two processes in creating continental crust are debated, but fractional differentiation is thought to play the dominant role.

There is little evidence of continental crust prior to 3.5 Ga. About 20% of the continental crust’s current volume was formed by 3.0 Ga.

During this time interval, about 60% of the continental crust’s current volume was formed. The remaining 20% has formed during the last 2.5 Ga.

Proponents of a steady-state hypothesis argue that the total volume of continental crust has remained more or less the same after early rapid planetary differentiation of Earth and that presently found age distribution is just the result of the processes leading to the formation of cratons (the parts of the crust clustered in cratons being less likely to be reworked by plate tectonics).

In contrast to the persistence of continental crust, the size, shape, and number of continents are constantly changing through geologic time. Different tracts rift apart, collide and recoalesce as part of a grand supercontinent cycle.

There are currently about 7 billion cubic kilometres (1.7 billion cubic miles) of continental crust, but this quantity varies because of the nature of the forces involved. The relative permanence of continental crust contrasts with the short life of oceanic crust.

Continental crust is rarely subducted (this may occur where continental crustal blocks collide and overthicken, causing deep melting under mountain belts such as the Himalayas or the Alps). For this reason the oldest rocks on Earth are within the cratons or cores of the continents, rather than in repeatedly recycled oceanic crust.

Continental crust and the rock layers that lie on and within it are thus the best archive of Earth’s history.

This results from the isostasy associated with orogeny (mountain formation). The crust is thickened by the compressive forces related to subduction or continental collision.

This forms a keel or mountain root beneath the mountain range, which is where the thickest crust is found. The thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust.

The high temperatures and pressures at depth, often combined with a long history of complex distortion, cause much of the lower continental crust to be metamorphic – the main exception to this being recent igneous intrusions. Igneous rock may also be “underplated” to the underside of the crust, i.e.

Continental crust is produced and (far less often) destroyed mostly by plate tectonic processes, especially at convergent plate boundaries. Additionally, continental crustal material is transferred to oceanic crust by sedimentation.

Also, material can be accreted horizontally when volcanic island arcs, seamounts or similar structures collide with the side of the continent as a result of plate tectonic movements. Continental crust is also lost through erosion and sediment subduction, tectonic erosion of forearcs, delamination, and deep subduction of continental crust in collision zones.

It is a matter of debate whether the amount of continental crust has been increasing, decreasing, or remaining constant over geological time. One model indicates that at prior to 3.7 Ga ago continental crust constituted less than 10% of the present amount.

The growth of continental crust appears to have occurred in spurts of increased activity corresponding to five episodes of increased production through geologic time.

The Earth can be divided into four main layers: the solid crust on the outside, the mantle, the outer core, and the inner core. Out of them, the mantle is the thickest layer, while the crust is the thinnest layer.

The crust’s thickness varies between some 10 km and just over 70 km, having an average of about 40 km. The core has, in total, a radius of 3500 km, but it is generally viewed as two distinct parts:

The mantle comprises about 83% of the Earth’s volume and around 68% of its mass. It is divided into several layers, based on different seismological characteristics (as a matter of fact, much of what we know about the mantle comes from seismological information — not from what we’ve observed directly).

Even though this area is regarded as viscous, you can also consider it as formed from rock: a rock called peridotite, to be more precise. A peridotite is a dense, coarse-grained igneous rock, consisting mostly of olivine and pyroxene, two minerals only found in igneous rocks.

But the Earth’s structure gets even more complicated. The crust is divided into tectonic plates, and those tectonic plates are actually thicker than the crust itself because they also encompass the top part of the mantle.

Scientific studies suggest that this layer has physical properties that are different from the rest of the upper mantle. Namely, the rocks in this part of the mantle are more rigid and brittle because of cooler temperatures and lower pressures.

Another way to think about it is that the crust and mantle are distinguished by composition, whereas the lithosphere (which includes the brittle upper portion of the mantle and the crust) and asthenosphere are defined by a change in mechanical properties. The upper mantle is what causes tectonic plates to flow.

This mixture is solid, but in time, it can flow. This flow is essential for life on Earth.

These currents move around hot material creating areas of upwelling and downwelling, which pull the tectonic plates around, causing them to interact and sometimes collide with each other.

Without this process, there would be no plate tectonics, and without plate tectonics, life as we know it wouldn’t exist — or at the very least, would be very different. The upper mantle also acts as a “reservoir” for molten rock, enabling it to rise to the surface through cracks and fissures in the Earth’s crust, through volcanic processes.

Some magma is rich in silica, which makes it more viscous, while other magma is low in silica, making it more fluid. Below that, there is the lower mantle – ranging from 670 to 2900 kilometers below the Earth’s surface.

The lower mantle is perhaps the least understood layer of our planet. We can’t survey it directly, we can only infer information about it from earthquakes and physics experiments where we simulate the conditions in the lower mantle.

We do know that the density and temperature of the mantle increase gradually towards the center, as does the velocity of seismic waves (a key parameter for studying the Earth’s internal structure). Mantle Trivia: Even though you can consider the mantle as molten rock or magma, modern research found that the mantle has between 1 and 3 times more water than all the oceans on Earth combined.

All the rock analysis, the drilling… everything we do is done in the crust. The deepest drill ever done is some 12 km below the surface… so how can we know the mantle.

As mentioned earlier, most of what we know about the mantle comes from seismological studies. When big earthquakes take place, the waves propagate throughout the Earth, carrying with them information from the layers they pass through – including the mantle.

However, the bulk of the information comes from seismic analysis. Seismic waves, just like light waves, reflect, refract, and diffract when they meet a boundary – that’s how we know where the crust ends and where the mantle begins, and the same goes for the mantle and the core.

In the mantle, temperatures range between 500 to 900 °C (932 to 1,652 °F) at the upper boundary with the crust. to over 4,000 °C (7,230 °F) at the boundary with the core.

How material flows towards the surface (because it is hotter and therefore less dense) while cooler material goes down. This process is still a matter of scientific debate, and there may be aspects of it we don’t fully understand (or don’t understand at all).

But earthquakes also happen deeper, at depths of over 300 km (the deepest recorded earthquake was 751 km deep). But rocks in the mantle can’t fault because of all the pressure, so how do earthquakes in the mantle take place.

It’s not clear why this happens, but several mechanisms have been proposed, including dehydration, thermal runaway, and mineral phase change. Basically, one mineral can morph into another when conditions change, and this can happen suddenly, in a fault-type fashion.

The deeper parts of our planet, the mantle, and the core, hide many more mysteries.

1 Earth is over 1200 km thick and has four layers. – Crust – outer solid rock layer (granite on land, basalt in oceans) – Mantle – thickest layer, mostly solid except for upper mantle that flows like “thick toothpaste” – Outer Core – made up of liquid iron and nickel – Inner Core – mostly solid iron, at high temperature and pressure FEATURES OF PLATE TECTONICS: 17.4-18.1.

3 The Asthenosphere is the molten (liquid) layer of the upper mantle Heat to keep the asthenosphere molten comes from radioactive elements Without radioactivity our planet would be cold and dead…. FEATURES OF PLATE TECTONICS.

– As magma is heated in the asthenosphere, convection currents drive plate movement. – Rising magma reaches the surface at ridges (in the oceans) or rifts (on land).

5 DATA BOOKLET PAGE 6-7 Tectonic plates are all moving at the same time There are 25 tectonic plates and many smaller ones. 6 Tectonic plates are all moving at the same time.

Data Booklet: p. 7 PLATE MOTION USGS.

8 DATA BOOKLET P. 6-7.

The denser oceanic plate subducts (gets pulled under) the less dense continental plate. – Large earthquakes and volcanoes are found in subduction zones.

10 3 FORCES THAT DRIVE PLATE TECTONICS 1. Convection Currents 2.

Slab Pull. 11 The Big Picture.

13 17.4-18.1 PLATE BOUNDARIES 1. Please collect the assignment for 17.4 and part of 18.1 from the front of the room 2.

Work with your neighbours to complete the assignment 4. The assignment is Due Next Class.

15 A plate boundary is an area where two plates touch. The way the plates interact is based on the type of plate and the direction the plates are moving.

16 Divergent plate boundaries – where plates spread apart Convergent Plate boundaries – where plates come together Transform plate boundaries – where plates move past each other PLATE INTERACTIONS. 17 1.

– Examples: Ocean ridges and continental rifts – The Mid-Atlantic Ridge is the longest mountain range on Earth. DIVERGENT PLATE BOUNDARIES.

There are 3 kinds. – Oceanic-continental – Oceanic-oceanic – Continental-continental CONVERGENT PLATE BOUNDARIES.

Cone-shaped volcanoes can form from magma seeping to the surface. Earthquakes happen when subduction, ridge push, and slab pull build pressure.

20 The cooler, denser plate will subduct under the less dense plate. – Convergence may make a volcanic island arc, Ex.

21 Since both are continental plates, their densities are similar. – As they collide, their edges fold and crumple, forming mountain ranges.

22 HIMALAYA’S The Himalayas are the world’s youngest (and tallest) mountain range, formed as Asia and Africa plates meet 40 million years ago. They are still growing taller today.

23 Where plates move past each other in opposite directions – Usually are found near ocean ridges – Since rock slides past rock, no mountains or volcanoes form TRANSFORM PLATE BOUNDARIES San Andreas fault.

As a result of studies during the past century, geologists have a pretty clear sense of what the layers inside the Earth are made of. Let’s now look at the properties of individual layers in more detail (figure above a, b).

As a result of studies during the past century, geologists have a pretty clear sense of what the layers inside the Earth are made of. Let’s now look at the properties of individual layers in more detail (figure above a, b).

The crust is our home and the source of all our resources. How thick is this all important layer.

An answer came from the studies of Andrija Mohorovicˇic´, a researcher working in Zagreb, Croatia. In 1909, he discovered that the velocity of earthquake waves suddenly increased at a depth of tens of kilometres beneath the Earth’s surface, and he suggested that this increase was caused by an abrupt change in the properties of rock.

Specifically, it’s deeper beneath continents than beneath oceans. Geologists now consider the change to define the base of the crust, and they refer to it as the Moho in Mohorovicˇic´’s honour.

In fact, the crust is only about 0.1% to 1.0% of the Earth’s radius, so if the Earth were the size of a balloon, the crust would be about the thickness of the balloon’s skin.

Geologists distinguish between two fundamentally different types of crust oceanic crust, which underlies the sea floor, and continental crust, which underlies continents.

At highway speeds (100 km per hour), you could drive a distance equal to the thickness of the oceanic crust in about five minutes. At the top, we find a blanket of sediment, generally less than 1 km thick, composed of clay and tiny shells that settled like snow out of the sea.

Most continental crust is about 35 to 40 km thick about four to five times the thickness of oceanic crust but its thickness varies significantly. In some places, continental crust has been stretched and thinned so it’s only 25 km from the surface to the Moho, and in some places, the crust has been crumpled and thickened to become up to 70 km thick.

On average, upper continental crust is less mafic than oceanic crust it has a felsic (granite-like) to intermediate composition so continental crust overall is less dense than oceanic crust. Notably, oxygen is the most abundant element in the crust (figure above).

Most continental crust is about 35 to 40 km thick about four to five times the thickness of oceanic crust but its thickness varies significantly. In some places, continental crust has been stretched and thinned so it’s only 25 km from the surface to the Moho, and in some places, the crust has been crumpled and thickened to become up to 70 km thick.

On average, upper continental crust is less mafic than oceanic crust it has a felsic (granite-like) to intermediate composition so continental crust overall is less dense than oceanic crust. Notably, oxygen is the most abundant element in the crust (figure above).

In terms of volume, it is the largest part of the Earth. In contrast to the crust, the mantle consists entirely of an ultramafic (dark and dense) rock called peridotite.

Researchers have found that earthquake-wave velocity changes at a depth of 400 km and again at a depth of 660 km in the mantle. Based on this observation, they divide the mantle into two sublayers: the upper mantle, down to a depth of 660 km, and the lower mantle, from 660 km down to 2,900 km.

Almost all of the mantle is solid rock. But even though it’s solid, mantle rock below a depth of 100 to 150 km is so hot that it’s soft enough to flow.

Soft here does not mean liquid. it simply means that over long periods of time mantle rock can change shape without breaking.

We used the word “almost” because up to a few percent of the mantle has melted. This melt occurs in films or bubbles between grains in the mantle at a depth of 100 to 200 km beneath the ocean floor.

The warmer regions are less dense, while the cooler regions are denser. The distribution of warmer and cooler mantle indicates that the mantle convects like water in a simmering pot.

The Core Early calculations suggested that the core had the same density as gold, so for many years people held the fanciful hope that vast riches lay at the heart of our planet. Alas, geologists eventually concluded that the core consists of a far less glamorous material, iron alloy (iron mixed with tiny amounts of other elements).

The outer core consists of liquid iron alloy. It can exist as a liquid because the temperature in the outer core is so high that even the great pressures squeezing the region cannot keep atoms locked into a solid framework.

The inner core, with a radius of about 1,220 km, is a solid iron alloy that may reach a temperature of over 4,700°C. Even though it is hotter than the outer core, the inner core is a solid because it is deeper and is subjected to even greater pressure.

Early calculations suggested that the core had the same density as gold, so for many years people held the fanciful hope that vast riches lay at the heart of our planet. Alas, geologists eventually concluded that the core consists of a far less glamorous material, iron alloy (iron mixed with tiny amounts of other elements).

The outer core consists of liquid iron alloy. It can exist as a liquid because the temperature in the outer core is so high that even the great pressures squeezing the region cannot keep atoms locked into a solid framework.

The inner core, with a radius of about 1,220 km, is a solid iron alloy that may reach a temperature of over 4,700°C. Even though it is hotter than the outer core, the inner core is a solid because it is deeper and is subjected to even greater pressure.

So far, we have identified three major layers (crust, mantle, and core) inside the Earth that differ compositionally from each other. Earthquake waves travel at different velocities through these layers.

In this context, we distinguish between rigid materials, which can bend or break but cannot flow, and plastic materials, which are relatively soft and can flow without breaking.

In other words, the Earth has an outer shell composed of rock that cannot flow easily. This outer layer is called the lithosphere, and it consists of the crust plus the uppermost, cooler part of the mantle.

Note that the terms lithosphere and crust are not synonymous the crust is just the upper part of the lithosphere. The lithosphere lies on top of the asthenosphere, which is the portion of the mantle in which rock can flow.

Geologists distinguish between two types of lithosphere (figure above). Oceanic lithosphere, topped by oceanic crust, generally has a thickness of about 100 km.

Notice that the asthenosphere is entirely in the mantle and generally lies below a depth of 100 to 150 km. We can’t assign a specific depth to the base of the asthenosphere because all of the mantle below 150 km can flow, but for conve.

Do the Atlantic Ocean and the Pacific Ocean Mix. Types of Agate With Photos Rubellite – Properties, Value, Occurrence and Uses New York Rockhounding – Places to Dig for Crystals in New York Types of Opal With Photos The Mystery of the Copper Scorpion.

Do the Atlantic Ocean and the Pacific Ocean Mix.

Do the Atlantic Ocean and the Pacific Ocean Mix.

Types of Agate With Photos.

Rubellite – Properties, Value, Occurrence and Uses.

New York Rockhounding – Places to Dig for Crystals in New York.

Types of Opal With Photos.

The Mystery of the Copper Scorpion.

The Mystery of the Copper Scorpion.

The Ring of Fire.

The Rarest Mineral on Earth.

Scientists have long suspected that Earth’s inner core was made of two layers. But it wasn’t until ANU researchers took a closer look at what lies below that an “innermost inner core” was confirmed.

Their work revealed a distinct change in the structure of iron deep within the inner core at about 3,604 miles below the Earth’s surface. You may recall from earlier that the inner core consists of solid iron alloy.

But distinct structural changes were detected in this iron alloy that set apart the newly discovered innermost layer from the rest of the inner core.

Further examination of this tiny layer may provide additional details around how our planets formed.

Seismic monitoring allows us to gain a better understanding of Earth’s interior. This is made possible by measuring sound waves that are created by earthquakes and pass through Earth’s layers.

The recent discovery was made with the aid of a special search algorithm that researchers used to compare thousands of models of the inner core with decades worth of data on how long seismic waves take to travel through Earth. This data, gathered by seismograph stations all over the world, helped detect the changes in the structure of iron in the inner core.

Although this work is still being analyzed, the discovery of a new layer may pave the way for a new geological principle and prompt textbooks to be rewritten.

The lithosphere–asthenosphere boundary (referred to as the LAB by geophysicists) represents a mechanical difference between layers in Earth’s inner structure. Earth’s inner structure can be described both chemically (crust, mantle, and core) and mechanically.

The actual depth of the boundary is still a topic of debate and study, although it is known to vary according to the environment.

these are factors that affect the rheological differences in the lithosphere and asthenosphere.

The depth to the LAB can be estimated from the amount of flexure the lithosphere has undergone due to an applied load at the surface (such as the flexure from a volcano). Flexure is one observation of strength, but earthquakes can also be used to define the boundary between “strong” and “weak” rocks.

This criterion works particularly well in oceanic lithosphere, where it is reasonably simple to estimate the temperature at depth based upon the age of the rocks. The LAB is most shallow when using this definition.

the Basin and Range Province) the MBL is thinner than the crust and the LAB would be above the Mohorovičić discontinuity.

The lithosphere is unable to support convection cells because it is strong, but the convecting mantle beneath is much weaker. In this framework, the LAB separates the two heat transport regimes [conduction vs.

However, the transition from a domain that transports heat primarily through convection in the asthenosphere to the conducting lithosphere is not necessarily abrupt and instead encompasses a broad zone of mixed or temporally variable heat transport. The top of the thermal boundary layer is the maximum depth at which heat is transported only by conduction.

At depths internal to the TBL, heat is transported by a combination of both conduction and convection.

Colder temperatures at Earth’s shallower depths affect the viscosity and strength of the lithosphere. Colder material in the lithosphere resists flow while the “warmer” material in the asthenosphere contributes to its lower viscosity.

In practice, the RBL is defined by the depth at which the viscosity of the mantle rocks drops below ~ 10 21 P a ⋅ s. {\displaystyle 10^{21}Pa\cdot s.}.

However, mantle material is a non-Newtonian fluid, i.e. its viscosity depends also on the rate of deformation.

Another definition of the LAB involves differences in composition of the mantle at depth. Lithospheric mantle is ultramafic and has lost most of its volatile constituents, such as water, calcium, and aluminum.

The depth to the base of the CBL can be determined from the amount of forsterite within samples of olivine extracted from the mantle. This is because partial melting of primitive or asthenospheric mantle leaves behind a composition that is enriched in magnesium, with the depth at which the concentration of magnesium matches that of the primitive mantle being the base of the CBL.

The seismic LAB (i.e. measured using seismological observations) is defined by the observation that there exists seismically fast lithosphere (or a lithospheric lid) above a low-velocity zone (LVZ).

The cause of the LVZ could be explained by a variety of mechanisms. One way to determine if the LVZ is generated by partial melt is to measure the electrical conductivity of the Earth as a function of depth using magnetotelluric (MT) methods.

Because mantle flow induces the alignment of minerals (such as olivine) to generate observable anisotropy in seismic waves, another definition of the seismic LAB is the boundary between the anisotropic asthenosphere and the isotropic (or a different pattern of anisotropy) lithosphere.

The Gutenberg discontinuity coincides with the expected LAB depth in many studies and has also been found to become deeper under older crust, thus supporting the suggestion that the discontinuity is closely interrelated to the LAB. Evidence from converted seismic phases indicates a sharp decrease in shear-wave velocity 90–110 km below continental crust.

Beneath oceanic crust, the LAB ranges anywhere from 50 to 140 km in depth, except close to mid-ocean ridges where the LAB is no deeper than the depth of the new crust being created. Seismic evidence shows that oceanic plates do thicken with age.

Data from ocean seismometers indicate a sharp age-dependent LAB beneath the Pacific and Philippine plates and has been interpreted as evidence for a thermal control of oceanic-lithosphere thickness.

The LAB is particularly difficult to study in these regions, with evidence suggesting that the lithosphere within this old part of the continent is at it thickest and even appears to exhibit large variations in thickness beneath the cratons, thus supporting the theory that lithosphere thickness and LAB depth are age-dependent.

Beneath Phanerozoic continental crust, the LAB is roughly 100 km deep.

1 Earth’s Crust. 2 Convection currents.

Pangea – the idea that the all land masses on earth were once a single large land mass.

Then, it flows sideways, carrying the seafloor away from the ridge in both directions. Convection current – unequal distribution of heat in the mantel causes a net movement in a circular motion.

6 The Earth’s CRUST is the outer most part of the Earth’s surface.Average 32 km thick Thickest point 70 km (in mountains) Thinnest point 8 km (under ocean). 7 Plate tectonic – theory that Earth’s crust and part of the upper mantle are broken into sections called plates.

Asthenosphere – plastic like layer below the lithosphere. The ridged plates of the lithosphere “float” on the more plastic layer called the asthenosphere.

10 Deformation – The breaking, tilting, and folding of crustal rock due to crustal movement. (three types of forces) Compression – squeezing of earth’s crust that compacts the rock.

Tension – is the pulling apart of the earth’s crust. Divergent boundary.

Shearing – pushes rocks side by side in opposite directions. Transform boundary.

11 Convergent boundary Divergent boundary Transformation boundary. 12.

14 FAULTS Normal Fault – fault caused by tension stress that moves the hanging wall down relative to the foot wall.

16 In Lateral (strike-slip) faulting, the two blocks move either to the left or to the right relative to one another. Strike-slip faults are associated with crustal shear.

17 Thrust Fault – is formed when compression causes the hanging wall to slide over the foot wall. (almost horizontal movement).

=‘s fold decreased temp =‘s fault increased pressure =‘s fold decreased pressure =‘s fault rock type – brittle =‘s fault rock type – ductile =‘s fold time – greater the time =‘s fold time – less time =‘s fault. 19.

23 Fault block mountain is a mountain created by blocks of rock uplifted by normal faults.

25 End of chapter 10. 26 Folds – are bends in rocks without breaking folds have two parts Anticline – upward part of fold syncline – downward part of fold Anticline.

28 Plateau – is a large area of flat land that is raised high above sea level. Usually bordered by cliffs or mountains.

29 Domes – is the uprising area caused by magma. 30 Floating crust – less dense more dense.

Mapping the thickness of Earth’s crust, on land and in the oceans, allows us to understand fundamental geological and geographical observations, such as the location of mountain belts and the depth of the oceans.

Our understanding of the processes that lead to the formation of ocean basins and their continental margins has evolved significantly over the last 20 years, or so, and has been the focus of several previous Society Special Publications (SPs 167, 187, 282, 369, 476 between 2000 and 2018).

We continued mapping in order to produce a new global map of crustal thickness (Fig. 1).

It is derived from recent satellite-acquired gravity anomaly data in combination with innovative geophysical techniques. The colours in the map represent the thickness of the crustal-basement.

This map advances on the pioneering seismological mapping of the 1990s by being much higher resolution, courtesy of the global coverage of satellite gravity data (see Further Reading).

1: Global map of crustal-basement thickness (continental and oceanic) derived by OCTek gravity inversion. The map is overlain by a shaded-relief display of the gravity anomaly data, which enhances the underlying tectonic features.

The crustal-thickness map is the product of a geophysical modelling technique, which has acquired the shorthand name OCTek gravity inversion (Ocean Continent Transition Tectonics). Input to the modelling comprises satellite free-air gravity anomaly data, topography/bathymetry data and information about sediment thicknesses above crustal basement.

An illustrative summary of the modelling workflow is provided in figure 2. The modelling is iterative, seeking first to determine Moho depth and from that to determine crustal thickness and type.

Further technical details of the modelling technique can be found within the Further Reading, but it is worth drawing attention to two aspects that are distinctive and make the approach particularly suitable for investigating ocean basins and their margins (Fig.

2: Schematic outline of the OCTek gravity inversion method to determine Moho depth, crustal-basement thickness and lithosphere thinning-factor, using gravity anomaly inversion incorporating a lithosphere thermal correction and prediction of magmatic addition to the crust. Figure modified from Roberts et al.

In: McClay, K.R. & Hammerstein, J.A.

The global map resolves the majority of known oceanic areas with a crustal thickness of about 5 to7 km, that is, normal-thickness oceanic crust. Exceptions to this are: (i) known volcanic plateaus such as Iceland, Kerguelen and Ontong-Java.

(iii) micro-continental blocks such as Jan Mayen, the Seychelles-Mascarenes and possibly several others. Onshore crustal thickness has a ‘typical’ value of about 37.5 km, with thicker crust delineating the major orogenic belts and also the thick cratonic crust of Africa.

We would advise against taking the onshore results too literally, in terms of precise values, but we believe the first-order results to be reliable.

Traditionally plate restorations use present-day geomorphic features, such as coastlines and shelf-breaks as their continental constraint. Such features, however, evolve with time and are not necessarily in the same relative position now as they were at the time of continental separation.

We have illustrated this here with two examples that involve a more complex plate-restoration sequence than the traditionally-illustrated closing of the Atlantic. They are the Gulf of Mexico (Fig.

The first map for the Gulf of Mexico (Fig. 3a) shows a central oceanic core of the Gulf picked out by crust about 5 to 7 km thick (blue) and flanked on all sides by the thicker continental crust of North America, Mexico and Cuba.

This is seen even more clearly in the inset map in which the shading has been further accentuated.

3: Gulf of Mexico. (a) Map of crustal-basement thickness.

(b) Map of continental lithosphere thinning-factor. Small-circles of plate motion, centred on red pole of rotation, are aligned with the oceanic transform faults.

Section located as blue line in Figs 3a&d. (d) Two-stage plate-restoration for the Gulf of Mexico.

The importance of recognising transform faults is that these allow us to define the direction of plate motion during sea-floor spreading and opening of the Gulf of Mexico. The fact that they are visibly arcuate means that the pole of rotation for opening must lie nearby.

3b) shows another result from the gravity inversion, related to crustal thickness, known as continental lithosphere thinning-factor. This is a measure of how much the continental crust and lithosphere have been thinned by the process of rifting and breakup.

Overlain on this map are a set of concentric circles that have been constructed to align with the arc of the transform faults. At the centre of the concentric circles (red circle) lies the associated pole of rotation for the opening of the Gulf of Mexico.

The traditional pole does not align with the arcuate transform faults imaged by the gravity modelling. A cross-section extracted from the results of the gravity modelling is shown in figure 3c (located in Figs.

The cross-section shows bathymetry and sediment fill, both of which are input to the model, underlain by crustal basement and mantle, separated by the Moho. The Moho is predicted by the gravity model and from the position of the Moho the model predicts the thickness of crustal basement.

The final set of figures for the Gulf of Mexico (Fig. 3d) shows a new restoration sequence for the basin, which uses the new pole of rotation associated with the oceanic transform faults.

This rotational restoration removes most, but not all, of the oceanic crust within the Gulf of Mexico. Step 2 shows that a narrow approximately E-W band of oceanic crust remains at about 165 Ma, which must be closed by a S-N motion of the Yucatan/South American block, producing the final pre-rift restoration of Step 3.

The Earth’s structure is a fascinating and complex arrangement of layers that make up our planet’s interior. Understanding this structure is crucial for geologists and scientists as it provides insights into the Earth’s composition, behavior, and the processes that shape our planet.

Contents. The Earth’s interior can be divided into three main layers: the crust, the mantle, and the core.

The Earth’s structure and the interactions between these layers are responsible for various geological phenomena, including earthquakes, volcanic eruptions, and the movement of tectonic plates. The knowledge of the Earth’s interior structure is crucial for understanding and predicting these natural events, as well as for exploring the planet’s history and geology.

Major Elements and Minerals in Earth’s Composition: Distribution of Elements Within Earth’s Layers:

The layered structure of the Earth is a consequence of the physical and chemical processes that have occurred over billions of years, including planetary accretion, differentiation, and geological activity. Earth’s magnetic field is a crucial and complex feature that surrounds our planet.

Here’s an overview of Earth’s magnetic field: 1.

Magnetic Polarity: 3.

Magnetic Field Function and Importance: 5.

Understanding Earth’s magnetic field is essential for various scientific, technological, and environmental reasons. It is an integral part of the planet’s geology and plays a vital role in maintaining the conditions necessary for life on Earth.

The Earth has three main layers:.

Starting from the outermost layer, the Earth is composed of the crust, followed by the mantle, and finally the core.

The Earth’s crust is the thinnest of the three layers, and it is the solid surface where we stand and live. This rocky layer is divided into large pieces called tectonic plates.

However, the thickness of the crust varies depending on the location. In some areas, it is very thick, while in other areas it is very thin.

Oceans lie above a thinner type of crust, known as oceanic crust, which is generally submerged in water and not as thick as continental crust. The thinner areas of the crust can cause problems like earthquakes.

The two types of crust are very different from each other and are made up of different minerals and rocks. Continental crust is usually thicker and less dense than oceanic crust.

Also, continental crust is generally older than oceanic crust. Some areas of continental crust are more than 4 billion years old, while most oceanic crust is 200 million years old or younger.

The Earth’s mantle is the thickest of the three layers. It is made mostly of solid rock and behaves like a solid.

Due to convection currents, hot rock slowly rises while cooler rock falls.

Both iron and nickel are magnetic, contributing to the Earth’s magnetic field.

While iron is a common element on Earth, we have also discovered elements that are heavier than iron. This suggests that Earth was formed from the explosion of a supernova.

This eventually formed our planet. Elements heavier than iron only form during supernova explosions.

1 Geophysical PropertiesEarth’s Interior and Geophysical Properties. 2 Studying Rocks from Earth’s InteriorGeologists can’t sample rocks very far below Earth’s surface.

Some oil wells reach depths of 8 km. No well has ever reached Earth’s mantle.

3 The Deepest Scientific Well12 km deep Penetrated ancient Precambrian basement rocks Took 15 years to drill. 4 Second Deepest Well KTB hole in SE Germany Depth of 10 kmCost more than $ 1 billion Technically as complex as space exploration.

Evidence From Seismic Waves. 7 1.

8 “Artificially” Creating Seismic Waves Thumper Trucks. 9 Artificially Creating Seismic Waves “Elbow Grease”.

Seismic __________ Refraction Bending of Seismic WavesOccurs only if velocity differs in each layer (caused by density differences). 12 3.

Can infer depth of boundaries between layers. 13 Refraction Without an InterfaceIncreasing density in a thick layer of uniform rock Increase in velocity Curved paths from many small changes in direction as wave passes through many layers.

Earth’s Internal Structure. 15 Crust 1.

16 Mantle 2. _________ LithosphereUpper Mantle: Part of the ________________ (1) Crust and Upper Mantle.

17 Mantle 2. _________ Asthenosphere c.

(4) Rocks may have little strength and be capable of flowing. 18 Mantle 1.

19 Lithosphere and Upper MantleDefined by a decrease in P-wave velocities. 20 Earth’s Concentric Shell Structure Inferred from P- and P- Wave Velocity Variations.

The Core Shadow _________Zones:Seismic Waves do not reach certain areas on the opposite side of Earth from a large Earthquake Shadow. 22 (1) P-Wave Shadow Zone Refraction of P-waves when they encounter the core boundary Size and shape of core can be determined because the paths of P-waves can be accurately determined.

23 (2) S-Wave Shadow Zone Larger than the P-wave shadow zoneDirect S-Waves are not recorded in the entire region more than 103o from the epicenter Indicates that S-waves do not pass through the core at all. 24 (3) Conclusions two liquid solid Infer that the core has _____ partsOuter core is __________.

25 Composition of the CoreDensity is very high when averaged with crust and mantle Evidence for iron (a) Meteorites may represent basic material that created the solar system and 10% are composed of Fe and Ni (may represent the cores of fragmented planetismals and asteroids Seismic and density data along with assumptions based on meteorite composition, point to a largely iron core The presence of Earth’s magnetic field also suggests a metallic core.

26 The Core-Mantle BoundaryTransition Zone up 200 km thick Decrease in P-wave velocities Great changes in seismic velocity ULVZ may be due to hot core that partially melts overlying rock Less dense silicate “sediment” Iron silicates formed from reaction of lighter iron alloys in the liquid outer core reacting with silicates in the lower mantle Collects in uneven layers and is squeezed out of pore spaces Forms an electrically conductive layer and explains the low seismic velocities Both the mantle and core undergo convection.

27 A Faster Rotating Core Seismic waves indicate the core rotates 1o/year faster Solid line – Shows position of a point in the core relative to Earth’s surface Dashed line – Shows where the point was in 1900. 28 Isostasy equilibrium A.

Wood blocks float in water with most of their mass submerged Crustal blocks “float” on mantle in a similar way. The thicker the block the deeper it extends into the mantle.

29 Isostatic Adjustment rise sink Vertical Areas that lose mass _______.Areas that gain mass _______. Isostatic Adjustment _____________ movement to reach equilibrium _____________________: Depth where each column of rock is in balance with others.

Crustal Rebound ______ movements of the crustLoss of huge mass of ice (glaciers) at the end of the Pleistocene Epoch Upward. 31 Crustal Rebound in Canada and the northern United StatesRed contours show amount of uplift in meters since the ice disappeared.

32 Isostatic Adjustment Due to the “Underplating” TheoryRising blobs of magma accumulate at a the base of a continent The continent becomes thicker due to underplating. The thickened continental crust causes it to be out of isostatic equilibrium, so it rises.

33 Gravity Measurements A. Force of gravity is affected by the _________ between two masses and the masses of the two objects distance.

Gravity Meter (Gravitometer)Measures gravitational attraction between Earth at a specific location and mass within the instrument. 35 C.

Positive Gravity AnomalyHigher ______ than normal gravity measurements Can indicate location of metallic subsurface ores and rocks. 37 Positive Gravity AnomolyUplift creates a mountain range without a mountain root.

The central “column” has more mass.

Negative Gravity Anomaly1. A region with ________ gravity measurements low.

40 Negative Gravity AnomalyRegions with mass deficiencies Areas still experiencing isostatic rebound. 41 F.

42 Earth’s Magnetic Fieldouter Believed to be generated in the _______ core. 1.

Current along with Earth’s rotation create a magnetic field.

Magnetic Reversals: Evidence in sea-floor rocks. 44 Evidence of Magnetic Reversals in Lava Flows.

Magnetic Anomalies Higher 1. Positive Gravity Anomalies________ than normal.

Negative Magnetic AnomaliesLower ________ than normal Can be caused by downdropped fault blocks. 48 Earth’s Heat Buoys Up Its CrustNew Information Published in 2008 (June 23rd Journal of Geophysical Research).

The crust is the top layer of the earth’s surface it covers the Mantle, it is also the earth’s harder shell. We are living on the crust, without the crust all the life on the earth could not survive.

The crust is made of two parts, the oceanic crust and the continental crust. The thickness of the crust can be any thickness from 1 km to 80 km thick.

The Oceanic crust is under the ocean. The Oceanic crust is 4-7 miles(6-11 km) thick.

The Oceanic Crust is made of volcanic rocks like basalt. The oceanic crust has the average hardness of the Oceanic crust is 3g/cm³.

The earth’s crust is the thickest under the continents. The continental crust is about 20 to 25 miles (30 to 40 km) thick.

The rock that is in the Continental crust is older than the rocks in the Oceanic rock, some of the rocks in the continental crust are 3.8 billion years old. The continental crust is mainly made of igneous rocks.

The average hardness of the continental crust is2.7g/cm³.

The lithosphere and the asthenosphere are the two layers of the Earth closest to the surface. Wait, but wasn’t the crust the layer that’s closest to the surface.

In essence, the lithosphere is the Earth’s hard and rigid shell that encompasses the outermost rocky shell of the Earth (and other rocky bodies as well). The asthenosphere is a softer, more malleable layer that allows for the dynamic movement of the tectonic plates.

Here’s why this matters a lot to geologists — and should also matter to you. Table of Contents.

But where do the lithosphere and asthenosphere come in.

Well, there are two ways of looking at the layers of the Earth. The first is based on the layers’ chemical composition, or what they’re made from.

The crust and mantle are composition-based, while the lithosphere and asthenosphere are a mechanical classification. It’s important to keep in mind that the lithosphere includes the crust and the top (rigid) part of the mantle, while the asthenosphere includes the ductile part of the mantle.

So the terms “crust,” “mantle,” “lithosphere,” and “asthenosphere” do overlap a bit, but they refer to different aspects of Earth’s structure. Here’s how they differ, for the most part.

So everything we see on this surface is a part of the crust (or the lithosphere, depending on how you consider it). But this is just a thin part of the Earth.

So why go to all this trouble with a different classification.

Geologists are interested in the chemistry of the Earth, but they’re also very interested in the movement of the planet’s surface. The lithosphere and asthenosphere especially help geologists in the context of plate tectonics.

Think of it more as a jigsaw puzzle. These pieces, called tectonic plates, float on the asthenosphere’s flowing river.

The ground beneath you is floating.

And when they do. It results in natural phenomena like earthquakes, volcanic eruptions, and the creation of mountain ranges.

Enter the asthenosphere. It’s not solid like the lithosphere.

This isn’t lava, though. The asthenosphere consists of semi-molten rock, which can flow and move, albeit very, very slowly.

The asthenosphere plays a vital role. The moving and shifting in this layer influence the world you experience every day.

While the lithosphere gets the credit for the dramatic events, it’s the asthenosphere that’s the real power player behind the scenes. It’s in the asthenosphere that convection currents happen.

This movement pushes and pulls the lithosphere, making continents drift apart or come together. Think of the asthenosphere as the engine driving the motion of the tectonic plates.

” Well, think about it. The fruits you enjoy from volcanic soils, the gold or diamonds adorning your jewelry, even the threat of natural disasters in some regions—all can be traced back to the activities in the asthenosphere and the movement of the lithosphere.

While we can’t stop earthquakes or volcanic eruptions, insights into the asthenosphere’s workings can offer a heads-up. As you read this, the asthenosphere continues its subtle dance, moving and shaping our world.

From tapping into geothermal energy to disaster mitigation, geological research in the lithosphere and asthenosphere holds a lot of promise. In time, as technology and research progress, we might be able to delve even deeper, understanding the mysteries of this magnificent layer better.

In the meantime, if there’s only one lesson you take from the lithosphere and asthenosphere, let it be this. Our planet is a wonderfully complex system and there’s more than one way to look at it.

A strong quake in the last year of the NASA Mars InSight mission, enabled researchers at ETH Zurich to determine the global thickness and density of the planet’s crust. On average, the Martian crust much thicker than the Earth’s or the moon’s crust, and the planet’s main source of heat is radioactive.

After more than three years of daily monitoring and with the power levels decreasing on InSight’s seismometer, researchers were rewarded with data from a sizeable Marsquake in May 2022. The surface waves observed from this estimated 4.6 magnitude quake not only traveled from the quake’s source to the measuring station, they also continued to travel around the entire planet several times.

“From this quake, the largest quake recorded during the entire InSight mission, we observed surface waves that circled Mars up to three times,” says Doyeon Kim, seismologist and lead author of a study just published in the journal, Geophysical Research Letters. In order to gain information about the structure that the waves passed through, the researchers measured how fast these waves propagate at different frequencies.

These seismic velocities provide insights into the interior structure at different depths. Previously, observed surface waves from the two large meteorite impacts also allowed regional findings along their specific propagation paths.

Combining their newly obtained results with existing data on the gravity and topography of Mars, the researchers were able to determine the thickness of the Martian crust. It averages 42 to 56 kilometers (26–35 miles).

To put this into perspective, seismic data indicates that the Earth’s crust has an average thickness of 21 to 27 kilometers (13–17 miles), while the lunar crust, as determined by the Apollo mission seismometers is between 34 and 43 kilometers (21–27 miles) thick.

Generally, smaller planetary bodies in our solar system have a thicker crust than the larger bodies. Kim explains, “We were fortunate to observe this quake.

While Mars is smaller than the Earth, it transports seismic energy more efficiently.”. One of the most important results of this research concerns the difference between the northern and southern hemispheres of Mars.

it is particularly visible in images from Mars satellites. The northern hemisphere on Mars consists of flat lowlands, while there are high plateaus in the south.

“One might think that this difference could be explained by two different rock compositions,” says Kim. “One rock would be denser than the other.” While the composition may be the same in the north and south, the thickness of the crust varies.

Precisely what have the researchers have been able to prove. “Based on the seismic observations and the gravity data, we show that the density of the crust in the northern lowlands and the southern highlands is similar,” they write.

“This finding is very exciting and allows an end to a long-standing scientific discussion on the origin and structure of the Martian crust,” says Kim. After all, analysis of meteorite impacts on Mars last year already provided evidence that the crusts in the north and south are made of the same material.

Further conclusions can also be drawn from the thick Martian crust. “Our study provides how the planet generates its heat and explains Mars’ thermal history,” says Kim.

The study found that 50% to 70% of these heat-producing elements are found in the Martian crust. This high accumulation could explain why there are local regions underneath where melting processes may still be taking place today.

More information: Doyeon Kim et al, Global crustal thickness revealed by surface waves orbiting Mars, Geophysical Research Letters (2023). DOI: 10.22541/essoar.167810298.85030230/v1.

Provided by ETH Zurich.